1. Field of the Invention
This invention relates to a charge mosaic membrane, and more specifically to a charge mosaic membrane useful for the separation of an electrolyte or non-electrolyte or for desalination. This invention is also concerned with a process for the production of the charge mosaic membrane.
2. Description of the Related Art
Conventional charge mosaic membranes, in each of which a cationic polymer and an anionic polymer are alternately arranged, have the function that they can dialyze a low-molecular electrolyte therethrough but cannot dialyze a non-electrolyte. They are hence highly promising candidates for the desalination or desalting of seawater or the like and a variety of research has been conducted thereon.
Representative charge mosaic membranes include, for example, those produced by combining block copolymers A-C and B-C--which have been formed by block-copolymerizing mutually-incompatible polymers A and B with a third polymer C, respectively--at such a ratio as permitting the formation of a lamellar or cylindrical structure, followed by the introduction of anionic groups and cationic groups; and those obtained by forming an anionic polymer and a cationic polymer into a mosaicked, ultrathin, planar film on a liquid-permeable support and then allowing the cationic and anionic polymers to epitaxially grow as layers on the same ionic polymers of the film, respectively.
Formation of a lamellar or cylindrical structure by making use of phase separation between two types of block copolymers, however, involves substantial difficulty from the technical viewpoint. Because of a limitation imposed on the mixing ratio of both the block copolymers and the anisotropy of both the structures, it is difficult to have the polymers of the different types stacked as alternate layers in a cross-section of the resultant membrane and also to communicate a front side of the membrane with a back side of the membrane via layers of each of the two types of the block copolymers. Moreover, a structure formed by such phase separation is anisotropic. This makes it difficult to form the lamellar or cylindrical structure with controlled directionality.
Subsequent to the formation of such a structure, cationic and anionic groups have to be introduced. This makes the production process complex. Further, a limitation is imposed on the quantities of these ionic groups to be reacted.
According to the epitaxial growth, the layer of the respective ionic polymers is allowed to grow on a mosaic pattern. Very strict control is therefore required upon formation of the mosaicked, ultrathin film and also upon formation of the respective polymer layers of the cationic and anionic polymers. This conventional process is therefore not suited for the production of a membrane of a large area.
Whichever conventional process is used, the resulting membrane is very thin and has low strength so that it is impossible to form a relatively thick membrane having high strength and excellent performance.